This invention relates to flash units and more particularly to reflectors for dispersing light from a light source to match flash coverage to the coverage of a range of camera lens coverages and in particular to match coverages of a wide range of lens types.
In the past, various type reflectors have been used to illuminate camera subjects in an attempt to avoid shadows and to match the flash coverage to the lens coverage so as to avoid underexposed or dark regions on standard size photosensitive film types.
Studio lighting systems have included light reflectors configured as a parabolic dish with a center located flash tube socket. Such reflectors produce a light dispersion pattern which is brighter in the vicinity of the center of the parabolic dish and which is less bright at the edges of the dish.
It is also known to provide a variety of separate flash units for connection to camera bodies to produce a flash pattern from each of the separate flash units which is matched to different lens focal lengths connected to the camera body.
Other flash units combine horizontal and vertical bounce capabilities established by an adjustable mechanical mount which provides rotation and tilting of the reflectors as well as zoom positioning of the reflector to cover a wide range of lens types.
Other flash units, all parabola based reflectors, include retractable wide angle diffusers which will disperse light from a reflector matched to a normal angle lens so as to match the reflector to wider angle lenses.
Another category of flash tube/reflector assemblies is used to concentrate light from a pulsed plasma source for generating a laser beam therefrom. Such assemblies have reflectors which are horizontally linear and operative to concentrate light from a light source in a desired manner. In certain of the prior art assemblies such concentration is obtained by use of reflectors having an involute shape to concentrate radiating plasma energy from a flash tube to the laser source. Examples of such reflector/collector assemblies are set forth in U.S. Pat. No. 4,002,499 issued July 26, 1974 for Radiant Energy Collector; U.S. Pat. No. 4,327,969 issued May 4, 1984 for Radiation Concentrator and Distributor; and U.S. Pat. No. 4,641,315, issued Feb. 3, 1987, for Modified Involute Flashlamp Reflector. Another patent showing a reflector with involute sections is set forth in U.S. Pat. No. 4,116,540 to Winston, issued in 1978.
None of the aforesaid prior art patents have a pair of reflector surfaces which are of involute section bent horizontally to extend the dispersion of reflected light. Specifically, they do not disclose flash units with reflectors configured to match the coverage of wide angle lens. The reflector system of the present invention is a wide angle flash reflector and has an improved performance compared to a parabola. The 35 mm format is considered herein only for presentation simplicity (it being understood that the system of the present invention will work in any format). The 35 mm focal length lens is the longest focal length lens considered (slightly) wide angle. A known parabola type reflector, on the other hand, cannot cover a 28 mm lens view without a diffusing filter.
In accordance with my invention, a reflector is configured to have dual involute surfaces intersecting at a cusp and wherein each such surface is bent in the horizontal to define an extended reflection surface for a light source near the cusp to disperse visible light therefrom in an extended pattern matched to a range of lens coverages from wide angle to telephoto.
A feature of the present invention is to provide a reflector having an improved curved, dual involute surface for use in dispersing light in illumination products including vehicle headlamps, spotlights, studio lights, flash light systems, infrared heaters, street lights, curved florescent lights and any other illuminating situations wherein an extended dispersion of light is desirable.
Another feature of my invention is to provide such a curved, dual involute reflector in association with a light source that includes a plasma arc whose length can be adjusted to vary the amount of light reflected from the reflector.
Yet another feature of my invention is to provide an improved flash tube with means thereon to adjust the length of the plasma arc.
Still another aspect of my invention is to provide a flash tube of the type in the preceding paragraph wherein the flash tube includes movable anode and cathode electrodes located interiorly of the tube and means located exteriorly of the tube to adjust the position of such electrodes to control the distance therebetween so as to vary the length of the plasma arc within the tube when an ionization potential is imposed across the electrodes.
In a specific embodiment of the invention the reflector has first and second involute surfaces with edge boundaries thereon joined to form a cusp. Each of the involute surfaces are bent horizontally to locate the cusp therebetween in an arcuate path in a plane intersecting the involute surfaces.
A light tube is located adjacent the cusp for directing plasma energy against the involute surfaces for producing a reflected light pattern of a wide angle form established by the vertical extent of the individual involute surfaces and the aperture between the individual involute surfaces so as to disperse the light source in an extended field of illumination.
In the case of a flash assembly, the light pattern dispersion is configured to match the lens coverage of wide angle and normal lenses. In the case of wide angle lens use, the light pattern dispersion controls underexposure in the perimeter regions of most popular size photosensitive films.
The preferred embodiment of the reflector of my invention includes involute surfaces which are symmetrical with respect to a horizontal plane through the longitudinal axis of the flash tube. Furthermore, the involute surfaces are formed to have the outermost edge thereof laterally offset with respect to the cusp and the cusp defines a circle in a horizontal plane intersecting the involute surfaces.
The preferred embodiment of the flash tube includes a sealed vacuum tube of light transparent material. The flash tube is bent to conform to the curvature of the cusp. A cathode electrode is slidably supported inside one end of the sealed tube and an anode electrode is slidably supported inside the opposite end of the sealed tube. Each of the electrodes is connected to an extensible high voltage lead. The extensible lead imposes a high voltage pulse between the electrodes when the flash is triggered. The high voltage pulse produces a plasma arc between the electrodes. A magnet is mounted on the exterior of the tube to slide with respect to the tube so as to attract an electrode to change the length of the plasma arc and thereby change the intensity of the light directed against the reflector.
While the variable length plasm arc is shown in a curved tube suitable for particular use with the dual involute curved cusp reflector of the present invention it is equally suitable for use with other shapes of tubes including straight tubes used in connection with parabolic reflectors.